A method is provided for determining, for a fourth-generation computed tomography (CT) scanner that includes a third-generation X-ray source and detector system and a plurality fixed, sparse photon-counting detectors (PCDs), a position of each PCD of the plurality of PCI)s. The method includes determining, for a given PCD, a set of view angles at which the PCI) will cast a shadow on the third-generation detector determining, for each view, by analyzing projection data obtained from a reference scan, a corresponding shadow location on the third-generation detector caused by the given PCD generating, for each view, a line connecting a position of the X-ray source at the view angle, and a corresponding shadow location of the set of shadow locations determining locations of all intersection points of the set of lines and determining a PCD centerline of the given PCD based on the locations of the intersection points.
